senile

UK: /ˈsiːnaɪl/

US: /ˈsinaɪl, ˈsɛnaɪl/

US: (sē′nīl, -nil, sen′īl)

WordReference Random House Learner's Dictionary of American English © 2026

se•nile /ˈsinaɪl, ˈsɛnaɪl/   adj. 

1. showing a decline of physical strength or mental functioning as a result of old age or disease.

se•nil•i•ty /sɪˈnɪlɪti/  n. [uncountable] See -sene-.

WordReference Random House Unabridged Dictionary of American English © 2026

se•nile  (sē′nīl, -nil, sen′īl), adj. 

1. showing a decline or deterioration of physical strength or mental functioning, esp. short-term memory and alertness, as a result of old age or disease.
2. of or belonging to old age or aged persons;
   gerontological;
   geriatric.
3. Geography, Place Names [Physical Geog.] (of topographical features) having been reduced by erosion to a featureless plain that stands everywhere at base level. Cf. peneplain. 

n. 

4. a senile person.

• Latin senīlis old, equivalent. to sen(ex) old man (akin to senior) + -īlis -ile
• 1655–65

Collins Concise English Dictionary © HarperCollins Publishers::

senile / ˈsiːnaɪl/ adjective

1. of, relating to, or characteristic of old age
2. mentally or physically weak or infirm on account of old age

Etymology: 17th Century: from Latin senīlis, from senex an old man

senility / sɪˈnɪlɪtɪ/ noun